I don't know what's going on with the story quest shop. All I know is that I have a MLB Vine, and I bought all 5 copies from the shop in the span of 4 weeks or so. +35% elemental attack is not bad. +30% elemental attack gets into "Do I really want to use this?" territory. Whether you'd use her over Medusa depends on your assault skill and whether you have elemental advantage.